A molded article can be made from expandable synthetic resin particles, such as preformed polystyrene beads or pellets, by expanding the synthetic resin particles in a mold cavity of a two-part or multipart mold by application of heat and shaping or molding the synthetic resin particles against the individual mold wall portions, which are heated by hot steam fed to a steam compartment located on the exterior side of the walls, i.e. the walls of the steam chest mold. The expanded synthetic resin particles are fused together by steam fed into the mold cavity. Then the article formed in the mold is stabilized by cooling by evacuating the steam compartment and feeding in a fluid and the molded article is subsequently removed from the mold.
In the known process and apparatus the mold wall is cooled by spraying on water which should be cold or preheated water as described in German Open Patent Application 31 15 773.
The spraying of water as a coolant or as an additional medium assisting the cooling process has the disadvantage that a residue of steam used for fusing the particles making up the molded article is condensed in the molded article.
The molded article thus is removed from the mold in a moist and/or wet condition and/or with moisture or water on the surface.
The use of a coolant injected into the steam chamber or water sprayed in also has the considerable disadvantage that material contained in the water, especially calcium compounds can react with lubricants provided as layers on the particles and materials contained in the synthetic resin particles, to form thick and only very difficultly removable coatings on the back surfaces of the mold wall portion facing the steam compartment. Such coatings considerably reduce the heat transfer coefficient for heat transferred to the mold wall portion from the steam chamber and hence the thermal energy efficiency of the mold.